摘要：The uncertainty principle in quantum mechanics (also known as Heisenberg’s uncertainty princi- ple) states that you cannot predict, with perfect accuracy, both the position and momentum of a particle. In economics, we realise that we can predict the values of two macroeconomic indica- tors, the output gap and the fi scal stance, with only limited accuracy. We cannot estimate both indicators without taking into account the other parameter’s estimate. While the United States has recently used a huge fi scal stimulus to considerably increase GDP as well as potential out- put, Europe after the fi nancial crisis learned how austerity not only reduced current GDP, but also potential GDP and so-called structural fi scal balances, contrary to the intention of the European fi scal rules.
